R7 acts as a volume control feeding the 2nd stage. Though I must say it’s placement in the circuit is not ideal. IC1A could be overloading and adjusting R7 to a low setting wouldn’t resolve that clipping problem. R7 should have been placed right at the input, before C5, then connect C6 directly to output of 1st stage.

The input is also AC coupled, so what is the low cutoff bandwidth?
You’re a Ph.D.EE… you forgot this formula? 1/2piRC. R=100K, C=100pf f=15.923 Khz. Again, 15.9khz doesn’t even cover the audio band. 68pf would be a more appropriate value with the 100K resistor (23.4Khz). And if we’re really going to scrutinize this ckt, 100K is too high a value and noise will be too great. 10K would be better.

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